Feed screw device

ABSTRACT

A ring-like lubricant supply device  6  is fitted into a recess  4  of a nut member  2.  The lubricant supply device  6  contains a lubricant and is formed in an outer peripheral surface with notches  7.  Tubular members  8  each having an outer diameter larger than the diameter of the notch  7  are inserted into the notches, pushing and widening the notches  7  in a circumferential direction. One end of the tubular member  8  is fitted into a recess  9   b  of a retaining ring  9  and the retaining ring  9  is fixed to a nut member  2.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 08/877,518 filed Jun. 17,1997, the entire content and disclosure of which are incorporated hereinby reference. This application is also related to application Ser. No.09/809,262 filed Mar. 16, 2001, and application Ser. No. 09/985,385filed Nov. 2, 2001, both of which are also divisions of application Ser.No. 08/877,518 filed Jun. 17,1997.

Priority is claimed from Jun. 17, 1996, based on Japanese PatentApplication Nos. 8-155545 and 8-155546. Priority is also claimed fromJul. 18, 1996, based on Japanese Patent Application No. 8-189148.Certified copies of the priority documents were filed in parentapplication Ser. No. 08/877,518 on Sep. 22,1997.

BACKGROUND OF THE INVENTION

This invention relates to a feed screw device of a ball screw, squarethread, etc. Particularly, the invention relates to a feed screw devicethat can automatically supply a lubricant over a long term.

A conventional ball screw, a kind of feed screw device, is described inJapanese Utility Model Unexamined Publication Nos. Hei 7-4952 and6-47762, etc., for example.

This kind of ball screw comprises a spiral thread groove 50 a made inthe outer peripheral surface of a screw shaft 50 threadably engaging aspiral thread groove 51 a made in the inner peripheral surface of a nutmember 51 via a plurality of balls 52, as shown in FIG. 1, forconverting relative rotation of the screw shaft 50 to the nut member 51into relative displacement in an axial direction of the nut member 51via the balls 52.

An annular recess 53 is formed in both end parts of the inner diameterface of the nut member 51 (in FIG. 1, only the right end is shown), anda sealing member 54 is mounted on the recess 53.

The sealing member 54 is made from plastic containing a lubricant into aring shape, and a projection 54 a that can be fitted into the threadgroove 50 a of the screw shaft 50 projects from the inner peripheralsurface of the sealing member.

A ring-like garter spring 55 is inserted in the circumferentialdirection between the outer peripheral surface of the sealing member 54and the recess 53 of the nut member 51. The garter spring 55 clamps downall the outer peripheral surface of the sealing member 54 toward theouter peripheral surface of the screw shaft 50, that is, the sealingmember 54 is pressed in the inner diameter direction.

Further, a tapped hole 56 radially penetrating the circumferential wallof the nut member 51 is made in the position of the recess 53 in the nutmember 51 and a set screw 57 is fitted into the tapped hole 56, therebyfixing the sealing member 54 to the nut member 51.

The garter spring 55 sets the gap between the inner peripheral surfaceof the sealing member 54 and the outer peripheral surface of the screwshaft 50 to zero or less for preventing the lubricant filled in the ballscrew from leaking to the outside and a foreign material from enteringthe ball screw from the outside.

Further, the lubricant exuding from the sealing member 54 decreasesfrictional resistance of the slide portion between the inner peripheralsurface of the sealing member 54 and the outer peripheral surface of thescrew shaft 50, namely, slide torque and at the same time, is suppliedto the thread groove 50 a of the screw shaft 50, the balls 52, and thethread groove 51 a of the nut member 51.

However, for the conventional feed screw device of the structure asdescribed above, the garter spring 55 needs to be inserted between theouter periphery of the sealing member 54 and the recess 53 of the screwshaft 50 so that a dimension error of the sealing member 54 is absorbedand that the inner peripheral surface of the sealing member 54 comes insliding contact with the outer peripheral surface of the screw shaft 50;it is feared that the outer diameter of the feed screw device may growas large as the garter spring.

In the conventional structure, the sealing member 54 is presseddiametrically, so that it is abutted against the outer peripheralsurface of the screw shaft 50, thus the spring needs to be disposed onall the outer periphery of the sealing member 54 in the circumferentialdirection.

The inner diameter portion on the opposite side (portion not pressed bythe garter sprint) to the side pressed by the garter spring 55 of thesealing member 54 in the axial direction apts to float-up with respectto the outer peripheral surface of the screw shaft and it is feared thata sufficient lubricant will not be supplied from the portion.

Some conventional feed screw devices comprise a spring inserted betweenthe tip of the set screw 57 and the sealing member 54 in place of thegarter spring 55. However, the lubricant supply section is also pressedonly diametrically, thus it is feared that the inner peripheral surfaceof the sealing member 54 may be placed out of contact with the outerperipheral surface of the screw shaft 50 or that the portion pressed bythe set screw in sliding contact with the screw shaft may be worn on oneside in portions shifted 90 degrees from the placement position of theset screw 57, etc., for example.

Even if hardware for suppressing jump out of the sealing member 54 fromthe recess 53 is attached to the nut member 51, the tapped hole 56 needsto be made in the nut member 51 and fixed by the set screw 57 to preventaccompanying rotation of the screw shaft 50 of the sealing member 54 inaddition to the hardware; workability is poor.

Further, when the sealing member 54 has a part cut (for example, thesealing member 54 is made into c-shaped) because of attachment thereof,the inner peripheral surface of the sealing member 54 does not come insufficient contact with the screw shaft 50 and it is feared that asufficient lubricant will not be supplied from the sealing member 54depending on the operating condition.

Known as another ball screw, a kind of conventional feed screw device,is a device wherein a space 204 between a screw shaft 201 and a ballscrew nut 202 threadably engaged into the screw shaft 201 via a largenumber of balls 203 is filled with grease or lubricant, as shown in FIG.2. The ball screw is of seal type wherein an annular recess 205 is madein an end of the ball screw nut 202 and a sealing member 206 is fittedinto the annular recess 205 to prevent powder dust, etc., from enteringinto the ball screw nut 202.

By the way, to lubricate such a conventional ball screw device, normallygrease or lubricant is supplied from a grease nipple 207 attached to theball screw nut 202 to a ball circulation passage for lubricating arolling element.

However, particularly when the ball screw device adopting such alubrication system directly using lubricant or grease is used in ahigh-temperature environment or a environment wherein wood chips, etc.,easily absorbing lubricants are existed, the filled lubricant or greaseflows out to the outside, is exhausted fast, and must be again suppliedrepeatedly for a short term. Japanese Utility Model UnexaminedPublication No. Hei 7-4952 is known as application relating to anoil-containing polymer lubrication ball screw to improve this point.

For the oil-containing polymer lubrication ball screw disclosed here, alubricant supply member mounted on a ball screw nut is formed oflubricant-containing rubber or synthetic resin and the lubricantcontinuously exuding from the lubricant supply member is automaticallysupplied to a rolling element lubrication passage of the ball screw nut.

However, with the ball screw, as the lubricant supply member containingthe lubricant runs with the ball screw nut while coming in contact withthe screw shaft, the lubricant exudes from the contact part forlubrication; lubricant supplied to a guide rail is easily absorbedparticularly in an environment wherein foreign materials such as woodchips easily absorbing lubricant are existed, and the lubricant can alsobe absorbed from the lubricant-containing polymer member; resultantly,it is feared that a lubrication failure may be invited.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a feed screwdevice for enabling a lubricant-containing member to come in uniformcontact with an outer peripheral surface of a screw shaft withoutenlarging the outer diameter of the feed screw device and in a simplestructure.

According to the invention, there is provided a feed screw devicecomprising a screw shaft, a nut member threadably engaging an outerperiphery of the screw shaft, and a lubricant supply device being fixedto the nut member, coming in contact with the outer peripheral surfaceof the screw shaft, and having a predetermined elastic force, wherein atleast the portion of the lubricant supply device facing the screw shaftis rubber or synthetic resin containing a lubricant, wherein a notch ismade in the outer periphery of the lubricant supply device, and whereinan expansion member fitted at least with the notch pressed in thecircumferential direction of the lubricant supply device is insertedinto the notch.

In the structure, when the expansion member is inserted into the notchof the lubricant supply device, it causes the notch to push and widen atleast the outer periphery of the lubricant supply device in thecircumferential direction.

Thus, a compression force along the circumferential direction acts onthe inside of the outer periphery of the lubricant supply device, atleast deforming all the inner peripheral surface in the inner diameterdirection. Resultantly, the inner diameter of the lubricant supplydevice is reduced for absorbing a dimension error of the lubricantsupply device, and the inner peripheral surface of the lubricant supplydevice comes in contact with the outer peripheral surface of the screwmember.

As the feed screw device is driven, a lubricant contained in thelubricant supply device exudes gradually over time, whereby slideresistance between the outer peripheral surface of the screw member andthe inner peripheral surface of the lubricant supply device is decreasedand as the feed screw device is driven, a lubricant is supplied to theouter peripheral surface of the screw member.

In the feed screw device according to the present invention, all theinner peripheral surface of the lubricant supply device can be broughtinto contact with the outer peripheral surface of the screw shaft byonly inserting the expansion member into a part of the lubricant supplydevice (notch), so that any member, such as a garter spring to beinstalled on all the outer peripheral surface of the lubricant supplydevice which was needed by the conventional lubricant supply device canbe eliminated.

In the case where the expansion member is formed with a projection whichis projected from a part of the outer peripheral surface of thelubricant supply device and is fitted into a part of the nut member,etc., it is possible that the expansion member also serves prevention ofrotation of the lubricant supply device.

In addition, according to the invention, there is provided in a screwtransmission device comprising a screw shaft, a nut member threadablyengaging an outer periphery of the screw shaft, and a ring-likelubricant supply device being disposed in the nut member with one axialend face opposed axially to the nut member and an inner peripheralsurface opposed to an outer peripheral surface of the screw shaft,wherein at least the portion of the lubricant supply device facing thescrew shaft is rubber or synthetic resin containing a lubricant, theimprovement which comprises a press member having a portion opposedaxially to an axial opposed end face of the lubricant supply device andbeing fixed to the nut member and a projection projecting from the pressmember to the lubricant supply device and inserted into the lubricantsupply device.

Further, in the screw transmission device, at least two projections canalso be provided and inserted into the lubricant supply device so thatpilot pressure in the circumferential direction is put on the lubricantsupply device as load.

In the structure, the device is sandwiched between the press member andthe nut member, so that an axial movement of the lubricant supply devicerelative to the nut member is restricted and the projection projectingfrom the press member prevents the lubricant supply device from rotatingwith the screw shaft.

That is, an axial movement and rotation of the lubricant supply devicecan be prevented by only fitting the press member having the projection.

As the screw transmission device is driven, a lubricant contained in thelubricant supply device exudes gradually over time, so that slideresistance between the outer peripheral surface of the screw member andthe inner peripheral surface of the lubricant supply device is decreasedand as the screw transmission device is driven, a lubricant is suppliedto the outer peripheral surface of the screw member.

Here, a pair of the projections may be provided approaching each otherand the projection span may be set smaller than the span between thepaired projection insertion positions disposed in the lubricant supplydevice. In doing so, by sandwiching between the paired projections,pilot pressure in the circumferential direction is put as load and sucha force to hold down the screw shaft acts on the inner peripheralsurface of the lubricant supply device.

Further, it is another object of the invention to provide a long-lifefeed screw device stable over a long term by automatically replenishinga lubricant supply member with a lubricant for suppressing occurrence ofa lubrication failure.

To the end, according to a second aspect of the invention, there isprovided, in a feed screw device comprising a screw shaft, a screw nutthreadably engaging an outer periphery of the screw shaft, and alubricant supply device being disposed at both ends of the screw nut forsealing the gap opening between the screw nut and the screw shaft, theimprovement wherein the lubricant supply member is made of alubricant-containing polymer member, the lubricant-containing polymermember being formed with lubricant reserve parts.

According to invention, the lubricant-containing polymer member sealsboth the ends of the screw nut and shuts off the inside of the screw nutfrom the external atmosphere, whereby even if the feed screw device isused in the external atmosphere which is of a bad environment whereinwood chips, etc., easily absorbing lubricant are existed, the inside ofthe screw nut is protected against the wood chips, etc., and the smoothlubrication effect can be maintained over a long time.

As a lubricant exudes from the lubricant-containing polymer member andis consumed, the lubricant-containing polymer member is replenished witha new lubricant sealed in the lubricant reserve parts, so that thelubricant exudes from the lubricant-containing polymer member over along time even in atmosphere wherein wood chips, etc., easily absorb thelubricant supplied to a guide rail, so that stable lubrication can becarried out for a long time.

If foreign materials such as wood chips are deposited on thelubricant-containing polymer member and the lubricant is absorbed fromthe portion, the lubricant-containing polymer member is replenished witha lubricant from the lubricant reserve parts, thus it is not feared thata lubrication failure will be invited.

Specifically, the lubricant reserve parts formed in the lubricant supplydevice may be lubricant reserve holes made near the sealed face of thescrew shaft or a lubricant reserve peripheral groove extendingsurrounding the screw shaft. If an annular recess is made in the screwnut and the lubricant supply member is fitted into the annular recessand the lubricant reserve holes or the lubricant reserve peripheralgroove is closed on the inner peripheral surface or bottom face of therecess, a lubricant filled in the lubricant reserve holes or thelubricant reserve peripheral groove can be sealed by a simple structure.

If the lubricant reserve peripheral groove is formed, thelubricant-containing polymer member is replenished uniformly with a newlubricant sealed in the lubricant reserve peripheral groove, thus stablelubrication can be carried out for a long time. If a plurality of thelubricant reserve holes are made in the circumferential directionsurrounding the screw shaft, the lubricant-containing polymer member isreplenished uniformly with a new lubricant in the lubricant reserveholes, thus stable lubrication can be carried out for a long time.

If a reinforcing plate is disposed overlapping the lubricant-containingpolymer member so as to shut off the lubricant-containing polymer memberfrom the external atmosphere, it prevents wood chips, dust, etc., fromcoming in contact with the lubricant-containing polymer member, so thatabsorbing the lubricant in wood chips, dust, etc., from the portion canbe prevented. If a reinforcing plate is disposed so that a compressionforce acts on the lubricant-containing polymer member, thelubricant-containing polymer member can be adjusted in hardness andinsufficient strength by the reinforcing plate, and breakage, cracks,etc., of the lubricant-containing polymer member can be prevented. Sincethe reinforcing plate is provided, a metal reinforcing plate (mandrel)need not be used; a problem of adhesion between the lubricant-containingpolymer member containing a large amount of lubricant and the metalreinforcing plate need not be considered.

Further, if the lubricant-containing polymer member is formed withcommunication holes from the lubricant reserve parts (lubricant reserveholes, lubricant reserve peripheral groove) to the face coming incontact with the screw shaft, the lubricant sealed in the lubricantreserve parts flows out into the screw shaft through the communicationholes. Thus, an appropriate lubricant-containing polymer member isprovided for a device requiring a large amount of lubricant.

For example, a lubricant-containing polymer member can be adopted as thelubricant supply device containing a lubricant according to theinvention.

For example, the product manufactured in the following manner can beused as the lubricant-containing polymer member: Any of paraffinhydrocarbon oil such as polyolefin oil, naphthene hydrocarbon oil,mineral oil, ether oil such as dialkyl diphenyl ether oil, or ester oilsuch as phthalate ester or trimellitate is mixed as a lubricant with apolymer selected from the group consisting of polyolefin polymersbasically having the same chemical structure such as polyethylene,polypropylene, and polymethylpentane and the mixture is fused, thenpoured into a predetermined mold and cooled and fixed under pressure.

Various additive agents such as an antioxidant, a rust preventive, awear inhibitor, a defoaming agent, and an extreme pressure agent may bepreviously added to the mixture.

The percentage composition of the lubricant-containing polymer membermay be set to 20%-80% by weight of polyolefin polymer and 80%-20% byweight of lubricant with respect to all weight, because if thepolyolefin polymer is less than 20% by weight, hardness, strength, etc.,required as the lubricant supply device cannot be provided and if thepolyolefin polymer exceeds 80% by weight (the lubricant is less than 20%by weight), lubricant supply lessens and the slide torque reduction andlubricant supply effects decrease.

The above-mentioned polymers have the same basic structure and differ inaverage molecular weight, covering the range of 1×10³ to 5×10⁶. Amongthe polymers, those of comparatively low molecular weight ranging from1×10³ to 5×10⁵ and those of ultra high molecular weight ranging from1×10⁶ to 5×10⁶ are used solely or mixed as required.

To improve the mechanical strength of the lubricant supply device, thefollowing thermoplastic resin and thermosetting resin may be added tothe polyolefin polymer:

Resin such as polyamide, polycarbonate, polybutylene terephthalate,polyphenylene sulfide, polyether sulfone, polyether ether ketone,polyamide imide, polystyrene, or ABS resin can be used as thethermoplastic resin.

Resin such as unsaturated polyester resin, urea resin, melamine resin,phenol resin, polyimide resin, or epoxy resin can be used as thethermosetting resin.

The resins may be used solely or mixed.

Further, to disperse the polyolefin polymer and any other resin in amore uniform state, a proper compatibilization agent may be added asrequired.

In addition to the polyolefin polymer and lubricant combinations asdescribed above, polyurethane rubber cured in a grease-containingcondition can also be used as the lubricant-containing polymer, asdescribed below in detail:

Polyurethane rubber is a compound produced by reaction of polyisocyanatewith an activated hydrogen compound.

Tolylene diisocyanate (TDI), hexamethylene diisocyanate (MDI),prepolymer (MW1000-MW2000) produced by reaction of TDI and MDI with anactivated hydrogen compound, such as castor oil, or the like can be usedas polyisocyanate.

A long chain activated hydrogen compound such as hydrocarbon ofpolybutadiene, etc., polyether of polyoxypropylene, etc., caster oil orcaster oil series polyol, polyester, or polycarbonate, a polyhydroxycompound such as water or ethylene glycol, or a short chain activatedhydrogen compound such as amino alcohol, or polyamino compound can beused as the activated hydrogen compound.

Normal grease such as mineral oil or lithium soap grease can be used asthe grease.

In this case, preferably the percentage composition of thelubricant-containing polymer member may be set to 80%-40% by weight ofpolyurethane rubber and 20%-60% by weight of grease with respect to allweight. If polyurethane rubber is less than 40% by weight, necessaryhardness, strength, etc., cannot be provided.

If polyurethane rubber exceeds 80% by weight (grease is less than 20% byweight), lubricant supply lessens and the slide torque reduction effectdecreases.

BRIEF DESCRIPTION OF THE DRAWING

In the accompanying drawings:

FIG. 1 is a fragmentary sectional view to show the main part of aconventional ball screw;

FIG. 2 is a sectional view to show a conventional feed screw device;

FIG. 3 is an exploded perspective view to show the main part of a ballscrew according to a first embodiment of the invention;

FIG. 4 is a sectional view to show the main part of a ball screwaccording to the first embodiment of the invention;

FIGS. 5(a) and 5(b) are views to show a lubricant supply deviceaccording to the first embodiment of the invention; 5(a) and 5(b) are asectional view and a front view of the lubricant supply devicerespectively;

FIGS. 6(a) and 6(b) are views to show a retaining ring according to thefirst embodiment of the invention; 6(a) and 6(b) are a side view of theretaining ring and a front view from the outside of the retaining ring;

FIGS. 7(a) and 7(b) are illustrations to explain the effects of notchesand expansion members according to the first embodiment of theinvention; 7(a) shows a state before the expansion members are insertedand 7(b) shows a state after the expansion members are inserted;

FIG. 8 is a sectional view to show the main part of a ball screwaccording to a second embodiment of the invention;

FIGS. 9(a) and 9(b) are views to show a lubricant supply deviceaccording to the second embodiment of the invention; 9(a) and 9(b) are asectional view and a front view of the lubricant supply devicerespectively;

FIGS. 10(a) and 10(b) are views to show an expansion member according tothe second embodiment of the invention; 10(a) and 10(b) are a side viewand a front view of the expansion member respectively;

FIGS. 11(a) and 11(b) are views to show a retaining ring according tothe second embodiment of the invention; 11(a) and 11(b) are a side viewof the retaining ring and a front view from the outside of the retainingring;

FIG. 12 is an exploded perspective view to show the main part of a ballscrew according to a third embodiment of the invention;

FIG. 13 is a fragmentary sectional view to show the main part of theball screw according to the third embodiment of the invention;

FIG. 14 is an exploded perspective view to show the main part of a ballscrew according to a fourth embodiment of the invention;

FIG. 15 is a sectional view to show the main part of the ball screwaccording to the fourth embodiment of the invention;

FIG. 16 is an illustration to explain the functions of projections andinsertion holes according to the fourth embodiment of the invention;

FIG. 17 is an exploded perspective view to show the main part of a ballscrew according to a fifth embodiment of the invention;

FIG. 18 is a sectional view to show the main part of the ball screwaccording to the fifth embodiment of the invention;

FIG. 19 is an exploded perspective view to show the main part of a ballscrew according to a sixth embodiment of the invention;

FIG. 20 is a sectional view to show another example of lubricant supplydevice;

FIG. 21 is a sectional view to show the main part of a ball screwaccording to a seventh embodiment of the invention;

FIG. 22 is a sectional view to show an inner diameter part of anotherexample of lubricant supply device;

FIG. 23 is a sectional view to show the main part of a ball screwaccording to an eighth embodiment of the invention;

FIG. 24 is a perspective view to show a lubricant-containing polymermember used in the eighth embodiment of the invention;

FIG. 25 is a perspective view to show a modified example of thelubricant-containing polymer member shown in FIG. 24;

FIG. 26 is a sectional view to show the main part of a ball screwaccording to a ninth embodiment of the invention;

FIG. 27 is a perspective view to show a lubricant-containing polymermember used in the ninth embodiment of the invention;

FIG. 28 is a perspective view to show a modified example of thelubricant-containing polymer member shown in FIG. 27;

FIG. 29 is a sectional view to show the main part of a ball screwaccording to a tenth embodiment of the invention;

FIG. 30 is a sectional view to show the main part of a ball screwaccording to an eleventh embodiment of the invention;

FIG. 31 is an illustration to show a first modified example of alubricant-containing polymer member formed with communication holesaccording to the invention;

FIG. 32 is an illustration to show a first modified example of alubricant-containing polymer member formed with communication holesaccording to the invention;

FIG. 33 is an illustration to show a first modified example of alubricant-containing polymer member formed with communication holesaccording to the invention;

FIG. 34 is a perspective view to show application of the invention to asingle axis actuator;

FIG. 35 is a front view to show a lubricant-containing polymer memberused with the single axis actuator in FIG. 34;

FIG. 36 is a sectional view taken on line C—C in FIG. 35;

FIG. 37 is a sectional view of the main part of a modified example oflubricant-containing polymer member according to the invention;

FIG. 38 is a sectional view of the main part of a modified example oflubricant-containing polymer member according to the invention;

FIG. 39 is a sectional view of the main part of a modified example oflubricant-containing polymer member according to the invention;

FIG. 40 is a sectional view of the main part of a modified example oflubricant-containing polymer member according to the invention; and

FIG. 41 is a sectional view of the main part of a modified example oflubricant-containing polymer member according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, there are shown preferredembodiments of the invention. In the embodiments, feed screw deviceswill be discussed by taking ball screws as examples. Of course, thedescription to follow goes for other feed screw devices such as squarethreads.

FIG. 3 is an exploded perspective view to show the main part of a ballscrew according to a first embodiment of the invention and FIG. 4 is asectional view of the main part.

First, a general configuration of the first embodiment will bediscussed. The ball screw comprises a nut member 2 threadably engagedinto a screw shaft 1 having a spiral thread groove 1 a on an outerperipheral surface via a large number of balls 3. The nut member 2 isformed in an inner peripheral surface with a thread groove 2 acorresponding to the thread groove 1 a of the screw shaft 1 and has aball circulation passage (not shown) for guiding and circulating theballs 3 rolling in both the thread grooves 1 a and 2 a in a thick barrelportion.

An annular recess 4 for attaching a lubricant supply device is formed inboth end faces of the inner diameter side of the nut member 2 coaxiallywith the nut member 2. Two tapped holes 5 are made in each of both theend faces of the nut member 2 with the axes parallel with the axis ofthe nut member 2. A lubricant supply device 6 is fitted into the recess4 of the nut member 2 coaxially.

The lubricant supply device 6 is a ring-like member having an outerdiameter that can be fitted into the recess 4, as shown in FIG. 5; forexample, it is made of a material such as rubber or synthetic resin forproducing a predetermined elastic force for providing flexibility andcontains a lubricant such as grease or mineral oil.

The lubricant supply device 6 has an assembly cut part 6 a at a place ina circumferential direction of the lubricant supply device 6 and isformed with notches 7 at outer peripheral positions shifted by 90degrees from the cut part 6 a in the circumferential direction, wherebythe two notches 7 are formed at symmetrical positions mutually shifted180 degrees in the circumferential direction. In the embodiment, thenotches 7 are made circular in cross section extending in a thicknessdirection of the lubricant supply device 6.

Further, projections 6 b that can be fitted into the thread groove 1 aof the screw shaft 1 project in the inner diameter direction on theinner peripheral surface of the lubricant supply device 6.

Tubular members 8 are included making up an expansion member that can befitted into the notches 7 of the lubricant supply device 6. The tubularmember 8 has an external diameter slightly larger than the diameter ofthe notch 7 and is slightly longer than the thickness of the lubricantsupply device 6.

Further, a retaining ring 9 is included for attaching the lubricantsupply device 6 to the nut member 2.

This retaining ring 9 has an inner diameter which is the same as thediameter of the nut member 2 and an inner diameter to place theretaining ring 9 out of contact with the outer peripheral surface of thescrew shaft 1, as shown in FIG. 4. In addition, as shown in FIG. 6, onthe face of the retaining ring 9 opposed to the nut member 2, throughholes 9 a are made at positions corresponding to the tapped holes 5 madein the nut member 2 and recesses 9 b into which the tubular members 8can be fitted are formed at positions corresponding to the notches 7 ofthe lubricant supply device 6.

First, the lubricant supply device 6 is fitted into the recess 4 and isinserted between the screw shaft 1 and the nut member 2, then thetubular members 8 are fitted into the notches 7 of the lubricant supplydevice 6 in parallel with the axis of the nut member 2. Alternatively,after the tubular members 8 are fitted into the notches 7, the lubricantsupply device 6 is fitted into the recess 4. In the state, the ends ofthe tubular members 8 fitted into the notches 7 project outward.

Successively, the projecting ends of the tubular members 8 are fittedinto the recesses 9 b of the retaining ring 9 and the retaining ring 9is abutted against the end of the nut member 2, then set screws 10inserted into the through holes 9 a of the retaining ring 9 arethreadably engaged into the tapped holes 5 of the nut member 2. Thus,the lubricant supply device 6 is fixed to the nut member 2, as shown inFIG. 4.

Here, the lubricant supply device 6 is formed only of alubricant-containing polymer, for example. To manufacture the lubricantsupply device 6, for example, a lubricant-containing polymer is fused,then injected into a predetermined metal mold, pressurized, cooled andhardened, and molded. In this case, injection molding can be executed.For example, used as the lubricant-containing polymer member is amixture of polyethylene consisting of 20% by weight of low molecularweight polyethylene (molecular weight 1×10³ to 5×10⁵) and 10% by weightof ultra-high molecular weight polyethylene (molecular weight 1×10⁶ to5×10⁶) and 70% by weight of paraffin mineral oil as a lubricant.

Next, the operation and effects of the ball screw will be discussed.

When the screw shaft 1 makes relative rotation to the nut member 2, theballs 3 in the nut member 2 roll on a spiral space formed by therelative thread grooves 1 a and 2 a in the rotation direction of thescrew shaft 1 and circulate through a ball circulation passage (notshown). As the balls 3 roll, the nut member 2 is fed in the lineardirection along the screw shaft 1. The projections 6 b of the lubricantsupply device 6 prevent the lubricant filled in the ball screw fromleaking to the outside and also prevent a foreign material such as dustfrom entering the ball screw from the outside; the lubricant supplydevice 6 also serves as a seal member.

Since the lubricant supply device 6 has a dimension error, it is fearedthat a microscopic gap may be formed between the inner peripheralsurface and the outer peripheral surface of the screw shaft 1. In theembodiment, however, the tubular members 8 larger than the notches 7 areinserted into the notches 7, whereby the notches 7 push and widen theouter periphery of the lubricant supply device 6 in the circumferentialdirection, as shown in FIG. 7.

That is, a compression force toward the circumferential direction actson the inside of the outer periphery of the lubricant supply device 6and causes the full inner peripheral surface to be displaced to theinner diameter side. Resultantly, even if a dimension error exists, thefull inner peripheral surface of the lubricant supply device 6 comes inreliable contact with the outer peripheral surface of the screw shaft 1.

At this time, in the embodiment, the lubricant supply device 6 is notpressed diametrically for bringing the inner peripheral surface intocontact with the outer peripheral surface of the screw shaft 1; instead,the compression force along the circumferential direction causes theinner peripheral surface to come in contact with the outer peripheralsurface of the screw shaft 1, thus the notches 7 need not be made in allthe peripheral surface of the lubricant supply device 6. Moreover, thetubular members 8 of expansion members are only inserted into thelubricant supply device 6, so that enlarging the diameter of the nutmember 2, namely, the outer diameter of the feed screw device is notrequired either.

Since the lubricant supply device 6 contains a lubricant, the lubricantexuding gradually from the inner peripheral surface of the lubricantsupply device 6 drastically reduces frictional resistance at the slidingtime between the inner peripheral surface of the lubricant supply device6 and the outer peripheral surface of the screw shaft 1, so that slidetorque lessens, preventing disturbance of drive of the ball screw.

Further, when the ball screw is driven, a lubricant exudes graduallyfrom the inner peripheral surface of the lubricant supply device 6 withrelative rotation of the screw shaft 1, is supplied to the thread groove1 a of the screw shaft 1, and uniformly covers the balls 3 rolling inthe thread groove 1 a and the thread groove 2 a of the nut member 2 forstable lubrication over a long term.

Therefore, even if a lubricant is not supplied to the inside of the nutmember 2 from the outside, the ball screw can continue good running fora long time at low torque. Since a lubricant need not be supplied to theinside of the nut member 2 from the outside, the ball screw can be usedas effective lubrication means in a system that can use only anextremely small amount of lubricant, such as a semiconductormanufacturing system.

Further, as described above, the tubular members 8 are inserted into thenotches 7, so that a compression force toward the circumferentialdirection acts on the inside of the lubricant supply device 6, alsoproducing the effect of bringing the opposed faces of the cut parts 6 amade in the lubricant supply device 6 into contact with each other orlessening the gap therebetween.

The ends of the tubular members 8 for pressing the inner peripheralsurface of the lubricant supply device 6 against the outer periphery ofthe screw shaft 1 are fitted only into the recesses 9 b of the retainingring 9, so that when the ball screw is driven, rotation of the lubricantsupply device 6 can be prevented. This means that the tubular members 8of expansion members also have a role in stopping rotation of thelubricant supply device 6.

Next, a second embodiment of the invention will be discussed. Membersidentical with or similar to those previously described in the firstembodiment are denoted by the same reference numerals in FIGS. 8 to 11.

The basic configuration of a ball screw of the second embodiment issimilar to that of the first embodiment, as shown in FIG. 8.

That is, as shown in FIG. 9, a lubricant supply device 6 is formed in anouter peripheral surface with three notches shifted by 90 degrees in thecircumferential direction, but is not formed on an inner peripheralsurface with projections 6 b fitted into thread groove 1 a of screwshaft 1.

Expansion members 12 inserted into the notches 7 are made of springmembers each having a slit 12 a along the axial direction, as shown inFIGS. 10(a) and 10(b), for easy assembling of the expansion members 12.

As shown in FIGS. 11(a) and 11(b), a retaining ring 9 has an outerdiameter that can be fitted into a recess 4 made in a nut member 2 andhas tapped holes 9 c, each with an axis directed diametrically, made inthe peripheral surface in place of through holes 9 a. Mounting holes 13each extending in the radial direction thereof so as to be coincidedwith the tapped holes 9 c are also made in the nut member 2. In FIG. 8,numeral 17 denotes a set screw mounted in the tapped hole 9 c and themounting hole 13.

Other components are similar to those of the first embodiment.

The second embodiment has the function and effects similar to those ofthe first embodiment.

The lubricant supply device 6 is not formed on the inner peripheralsurface with projections 6 b that can be fitted into the thread groove 1a of the screw shaft 1. However, the inner diameter of the lubricantsupply device 6 is shrunk by the action of the expansion members forpressing the inner peripheral surface of the lubricant supply device 6against the outer peripheral surface of the screw shaft 1, therebymaking contact.

Next, a third embodiment of the invention will be discussed. Membersidentical with or similar to those previously described in the firstembodiment are denoted by the same reference numerals in FIGS. 12 and13.

The basic configuration of a ball screw of the third embodiment issimilar to that of the first embodiment, as shown in FIGS. 12 and 13.

However, a lubricant supply device 6 is abutted against the end face ofa nut member 2 coaxially without forming the nut member 2 with a recessinto which the lubricant supply device 6 is fitted.

Tapped holes 15 are made at positions of the end face of the nut member2 corresponding to the positions of notches 7 made in the lubricantsupply device 6.

A retaining ring 9 is molded into a cap-shape that can store thelubricant supply device 6. Small-diameter tapped holes 16 directedtoward the outside from the bottom faces of recesses 9 b into whichtubular members 8 are fitted are made in place of through holes 9 a.

The tips of set screws 10 penetrating the tapped holes 16, the recesses9 b, and the tubular members 8 coaxially are threadably engaged into thetapped holes 15 of the nut member 2 for fixing the lubricant supplydevice 6.

Thus, without making recesses 4 in the nut member 2, the set screws 10for fixing the lubricant supply device 6 can be laid out at the samepositions as the placement positions of the tubular members 8 ofexpansion members.

However, at least the portion of the lubricant supply device 6 coming incontact with the outer peripheral surface of a screw shaft 1, namely,only the inner peripheral surface may be made of a member containing alubricant.

Further, the lubricant supply device 6 may have only the inner diameterside softened. In doing so, the hardness for holding the shape requiredas the lubricant supply device 6 can be provided on the outer peripheralsurface side and the displacement amount in the inner diameter directionon the inner peripheral side produced by a compression force along thecircumferential direction can be set large and press pressure againstthe outer peripheral surface of the screw shaft 1 can be set small.

Further more, although in the embodiments two or three notches 7 areprovided, one notch 7 or four or more notches 7 may be made. The notches7 need not be of the same shape.

The shape is not limited to circular cross section and may be angularcross section; the axis of the notch 7 need not necessarily be set inparallel with the axis of the nut member 2.

In the embodiments, the notches 7 are opened to the outer periphery ofthe lubricant supply device 6, but may be formed into a hole with theouter periphery side closed. However, the notch opened to the outerperiphery produces a larger effect.

The hollow tubular members are adopted for the expansion members as anexample, but the expansion members are not limited to them; they may belike a circular cylinder and the cross section is not limited to beingcircular.

Further, in the embodiments, the ends of the expansion members areprojected to the side of the retaining ring 9, but may be projected tothe side of the nut member 2 and the corresponding recesses may be madeon the side of the number member 2. A portion projecting toward theouter peripheral direction of the lubricant supply device 6 may be madeon the outer periphery of the expansion member for use as a rotationstopper.

In the embodiments, the lubricant supply device 6 also serves as a sealmember, but a separate seal member may be provided.

Next, a fourth embodiment of the invention will be discussed. Membersidentical with or similar to those previously described in the firstembodiment are denoted by the same reference numerals in FIGS. 14 to 16and will not be discussed again.

A lubricant supply device 106 has a cut part 106 a for assembly in thecircumferential direction and two insertion holes 107 made with the cutpart 106 a. The two insertion holes 107 are paired and are made so as toextend in parallel with the axis of the lubricant supply device 106. InFIGS. 14 and 15, the insertion holes are shown as through holes, but maybe holes each having the bottom surface.

Further, a fixed ring 108 for attaching the lubricant supply device 106to a nut member 2 is included. It provides a press member with onesurface facing the axial opposed end face of the lubricant supply device106.

The fixed ring 108 is a disk-like member having an inner diameter whichis the same as the outer diameter of the nut member 2 and an innerdiameter to place the fixed ring 108 out of contact with the outerperipheral surface of the screw shaft 1. On the face opposed to the nutmember 2, through holes 109 are made at positions corresponding totapped holes 5 made in the nut member 2. In addition, projections 110projecting toward the lubricant supply device 106 are formed atpositions corresponding to the insertion holes 107 of the lubricantsupply device 106.

The span between the two projections 110 is set slightly smaller thanthat between the paired insertion holes 107. In the embodiment, theprojection 110 is formed by cutting a part of the fixed ring 108 andbending the part to the lubricant supply device 106. That is, theprojections 110 can be made by press working, etc.

Assembling process of the lubricant supply device according to thefourth embodiment will be described hereinafter.

First, the lubricant supply device 106 is fitted into a recess 4 of thenut member 2 and is inserted between the screw shaft 1 and the nutmember 2. In the state, one axial end face of the lubricant supplydevice 6 is opposed axially to the bottom face of the recess 4 of thenut member 2 and the inner peripheral surface of the lubricant supplydevice 106 is opposed diametrically to the outer peripheral surface ofthe screw shaft 1.

Successively, the projections 110 of the fixed ring 108 are insertedinto the insertion holes 107 of the lubricant supply device 106 and setscrews 111 inserted into the through holes 109 are threadably engagedinto the tapped holes 5 with the outer periphery of the fixed ring 108abutted against the end of the nut member 2 coaxially, so that the fixedring 108 is fixed to the nut member 2.

Here, the lubricant supply device 106 is formed only of alubricant-containing polymer, for example. To manufacture the lubricantsupply device 106, for example, a lubricant-containing polymer is fused,then injected into a predetermined metal mold, pressurized, cooled andhardened, and molded. In this case, injection molding can be executed.For example, used as the lubricant-containing polymer member is amixture of polyethylene consisting of 20% by weight of low molecularweight polyethylene (molecular weight 1×10³ to 5×10⁵) and 10% by weightof ultra-high molecular weight polyethylene (molecular weight 1×10⁶ to5×10⁶) and 70% by weight of paraffin mineral oil as a lubricant.

Next, the operation and effects of the ball screw will be discussed.

When the screw shaft 1 makes relative rotation to the nut member 2,balls 3 in the nut member 2 roll on a spiral space formed by therelative thread grooves 1 a and 2 a in the rotation direction of thescrew shaft 1 and circulate through a ball circulation passage (notshown). As the balls 3 roll, the nut member 2 is fed in the lineardirection along the screw shaft 1. The inner peripheral surface of thelubricant supply device 106 prevents the lubricant filled in the ballscrew from leaking to the outside and also prevent a foreign materialsuch as dust from entering into the ball screw from the outside; thelubricant supply device 106 also serves as a seal member.

When the screw shaft 1 makes relative rotation to the nut member 2 andthen the nut member 2 is moved in the axial direction, rotation torqueand an axially external force are applied to the lubricant supply device106 as load.

However, in the embodiment, the lubricant supply device 106 issandwiched axially between the bottom face of the recess 4 of the nutmember 2 and the fixed ring 108, thus an axial movement of the lubricantsupply device 106 is blocked. Resultantly, jump out of the lubricantsupply device 106 from the nut member 2 can be prevented.

In addition, the projections 110 projected from the fixed ring 8 areinserted into the insertion holes 107 of the lubricant supply device106, so that rotation of the lubricant supply device 106 in thecircumferential direction can be prevented. Resultantly, when the screwshaft 1 rotates, the lubricant supply device 106 does not rotate withthe screw shaft 1 and comes in sliding contact with the outer peripheralsurface of the screw shaft 1.

At this time, since the lubricant supply device 106 contains alubricant, the lubricant exuding gradually from the inner peripheralsurface of the lubricant supply device 106 drastically reducesfrictional resistance at the sliding time between the inner peripheralsurface of the lubricant supply device 106 and the outer peripheralsurface of the screw shaft 1, so that slide torque lessens, preventingdisturbance of drive of the ball screw and lessening the rotation forceinput to the lubricant supply device 106.

Further, when the ball screw is driven, a lubricant exudes graduallyfrom the inner peripheral surface of the lubricant supply device 106with relative rotation of the screw shaft 1 as described above, issupplied to the thread groove 1 a of the screw shaft 1, and uniformlycovers the balls 3 rolling in the thread groove 1 a and the threadgroove 2 a of the nut member 2 for stable lubrication over a long term.

Therefore, even if a lubricant is not supplied to the inside of the nutmember 2 from the outside, the ball screw can continue good running fora long time at low torque. Since a lubricant need not be supplied to theinside of the nut member 2 from the outside, the ball screw can be usedas effective lubrication means in a system that can use only anextremely small amount of lubricant, such as a semiconductormanufacturing system.

Since the span between the projections 110 is set slightly smaller thanthat between the paired insertion holes 107 made in the lubricant supplydevice 106, the projections 110 inserted into the insertion holes 107give such pilot pressure F to make the opposed faces between the cutparts 106 a approach each other or press the opposed faces, as shown inFIG. 16. As a result of the pilot pressure F, even if the lubricantsupply device 106 contains a dimension error, such a force to hold thescrew shaft 1 acts, causing the inner peripheral surface of thelubricant supply device 106 to come in reliable contact with the outerperipheral surface of the screw shaft 1.

At this time, the lubricant supply device 106 is not presseddiametrically for bringing the inner peripheral surface of the lubricantsupply device 106 into contact with the outer peripheral surface of thescrew shaft 1 and such a force to hold the screw shaft 1 causes theinner peripheral surface of the lubricant supply device 106 to come incontact with the outer peripheral surface of the screw shaft 1. If theinsertion holes 107 and the projections 110 are not made on all theperiphery of the lubricant supply device 106 in the circumferentialdirection, all the inner peripheral surface of the lubricant supplydevice 106 can come in reliable contact with the screw shaft 1.Moreover, the insertion holes 110 are only inserted into the insertionholes 107 of the lubricant supply device 106, so that it is notnecessary to enlarge the diameter of the nut member 2, namely, the outerdiameter of the screw device.

By only assembling the fixed ring 108 having the projections 110 of asimple structure, jump out of the lubricant supply device 106 from thenut member 2 can be prevented, the lubricant supply device 106 can beprevented from rotating with the screw shaft 1, and the inner peripheralsurface of the lubricant supply device 106 can be brought into contactwith the outer peripheral surface of the screw shaft 1.

Note that a pipe-shaped spacer may be previously inserted into theinsertion hole 107 of the lubricant supply device 106 for preventingdistortion between the projection 110 and the insertion hole 107 whenrotation force is input.

In this embodiment, although a set of a pair of insertion holes and apair of projections is taken as an example, a set of two or more pairsof insertion holes or three or more insertion holes and two or morepairs of projections or three or more projections can be provided.

Next, a fifth embodiment of the invention will be discussed. Membersidentical with or similar to those previously described in the fourthembodiment are denoted by the same reference numerals in FIGS. 17 and18.

The basic configuration of a ball screw of the fifth embodiment issimilar to that of the fourth embodiment, as shown in FIGS. 17 and 18.

However, a plurality of lip parts 120 are projected along thecircumferential direction toward the inner peripheral surface of alubricant supply device 106 and come in sliding contact with the outerperipheral surface of a screw shaft 1.

A fixed ring 108 providing a press member has an outer diameter setslightly larger than the diameter of a recess 4 of a nut member 2 andhas a part cut in the circumferential direction instead of a throughhole 109 shown in the fourth embodiment. A pair of mounting holes 108 bare made in the proximity of the cut part 108 a.

A ring-like fit groove 121 into which the fixed ring 108 can be fittedis formed in the inner peripheral surface of the recess 4 of the nutmember 2.

After the lubricant supply device 106 is engaged into the recess 4, thefixed ring 108 is fitted into the fit groove 121 in the recess 4. To fitthe fixed ring 108, the mounting holes 108 b are used to lessen thedistance between the opposed faces of the cut part 106 a for reducingthe diameter of the fixed ring 8. In this state, the fixed ring 108 isinserted into the recess 4.

Also in this case, projections of the fixed ring 108 are inserted intoinsertion holes 107 of the lubricant supply device 106.

Other components and the function and effects of the fifth embodimentare similar to those of the fourth embodiment.

However, the portions of the lubricant supply device 106 coming incontact with the screw shaft 1 are formed as the lip parts 120 so as toprovide interference, so that the inner periphery of the lubricantsupply device 106 comes in reliable contact with the outer peripheralsurface of the screw shaft 1 even if pilot pressure F, etc., is notgiven. Thus, it is possible to eliminate the pilot pressure F.

Even if the interference state is set up, press pressure put on theouter peripheral surface of the screw shaft 1 is small, because the lipparts 120 can be warpped. No problem arises in this state.

In the fifth embodiment, the lubricant supply device 106 is engaged intothe nut member 2, thus set screws are not required.

Next, a sixth embodiment of the invention will be discussed. Membersidentical with or similar to those previously described in the fourthembodiment are denoted by the same reference numerals in FIG. 19.

The basic configuration of a ball screw of the sixth embodiment issimilar to that of the fourth embodiment, as shown in FIG. 19.

However, a plurality of lip parts 120 are provided along thecircumferential direction toward the inner peripheral surface of alubricant supply device 106, so that pilot pressure F need not be given,reducing the number of projections 110 formed on a fixed ring 108 toone.

Other components and the function and effects of the fifth embodimentare similar to those of the above-described embodiment.

However, in order to balance mounting, a set of insertion hole 107 andprojection 110 may also be made at points shifted 180 degrees in thecircumferential direction.

The lubricant supply devices of these embodiments may have noprojections on the inner peripheral surface or may be provided with aplurality of lip parts 20. However, the invention is not limited tothem. For example, a spiral projection 106 b that can be fitted into thethread groove 1 of the screw shaft 1 may be made on the inner peripheralsurface of the lubricant supply device, as shown in FIG. 20.

Next, a seventh embodiment of the invention will be discussed. Membersidentical with or similar to those previously described in the fourthembodiment are denoted by the same reference numerals in FIG. 21.

The basic configuration of a ball screw of the seventh embodiment issimilar to that of the above-mentioned embodiment, as shown in FIG. 21.

However, without forming a nut member 2 with a recess 104, a cap-shapedpress member 125 is formed and a lubricant supply device 106 is housedin the cap-shaped press member 125. At this time, a bottom 125 a of thecap-shaped press member 125 is opposed axially to the axial opposed endface of the lubricant supply device 106.

Other components and the function and effects of the seventh embodimentare similar to those of the above-described embodiment. However, in theseventh embodiment, the nut member need not be formed with the recess 4.

Further, a projection 110 is made on the bottom 125 a opposed axially tothe lubricant supply device 106 as in the above-described embodiment,but the invention is not limited to it. For example, the projection 110may be made on a circumferential wall portion 125 b opposed to thelubricant supply device 106 in the circumferential direction 6.

In the embodiments, a part of the press member of the fixed ring, etc.,is cut and the cut part is bent for forming the projection. However, theinvention is not limited to it. For example, the projection may beformed by welding etc., on the face opposed to the lubricant supplydevice or a hole may be made in the press member and a bar-like membermay be attached to the hole as a projection. However, if the projectionis formed by cutting a part of the press member and bending the cut partas described above, it can be manufactured by press working easily andat low costs.

In the embodiments, the insertion holes are made in the lubricant supplydevice and the projections are inserted into the insertion holes.However, the invention is not limited to it. For example, without makingthe insertion holes in the lubricant supply device, it is possible tomake the tips of the projections sharpen, in such a manner that theprojections may be stuck into the lubricant supply device for insertion.At this time, in the case where pilot pressure in the circumferentialdirection is preferably put as load, the projections may be stuck intothe lubricant supply device while the lubricant supply device is beingwarped in the circumferential direction.

In the embodiment, the lubricant supply device also serves as a sealmember, but a separate seal member may be provided.

The lubricant supply device may be divided into parts along thecircumferential direction. That is, the lubricant supply device may belike a ring as a whole. In this case, projections may be provided so asto connect the divisions or so as to correspond with the divisions.

Further, as shown in FIG. 22, the portion of the lubricant supply devicecoming in contact with the screw shaft 1 may be formed into a pluralityof lip parts 130 actually arranged.

Next, an eighth embodiment of the invention will be discussed.

FIG. 23 is a sectional view to show the main part of a ball screwaccording to the eighth embodiment of the invention to show a specificstructure of a feed screw device; the embodiment is applied particularlyto a seal-type ball screw.

In the embodiment, a spiral thread groove 201 b is formed in an outerperipheral surface 201 a of a screw shaft 201 and a ball screw nut 202is formed in an inner peripheral surface 202 a with a thread groove 202b corresponding to the thread groove 201 b. The ball screw nut 202 isthreadably engaged into the screw shaft 201 with a large number of balls203 disposed between the thread grooves 201 b and 202 b. Although notshown, a ball circulation section for guiding the balls 203 into thethread grooves 201 b and 202 b and rolling and circulating the balls isformed in the thick barrel portion of the ball screw.

The ball screw nut 202 is formed in an end face with an annular recess205 into which a lubricant-containing polymer member 210 is fitted. Thelubricant-containing polymer member 210 is an elastic member formed intoa cylindrical shape, is provided with a cut part 210 a along thesubstantially axial direction as shown in FIG. 24, and contains alubricant such as grease or mineral oil.

The lubricant-containing polymer member 210 formed into a cylindricalshape is provided on an inner peripheral surface with a projectionstripe 210 b to be fitted into the thread groove 201 b of the screwshaft 201 and formed in one end face 210 c with a plurality of lubricantreserve holes 210 d at positions distant from each other in thecircumferential direction.

The lubricant reserve holes 210 d are filled with a lubricant, an outerperipheral surface 210 e of the lubricant-containing polymer member 210is abutted against an inner peripheral surface 205 a of the recess 205made in an end face of the ball screw nut 202, and one end face 10 c ofthe lubricant-containing polymer member 210 is abutted against a bottomface 205 b of the recess 205. In this state, the projection stripe 210 bis fitted into the thread groove 201 b of the screw shaft 201, so thatthe lubricant-containing polymer member 210 is fitted into the recess205, as shown in FIG. 23. The ball screw nut 202 is formed with a tappedhole extending diametrically inward from the outer peripheral surfaceand opened at the recess 205. As shown in FIG. 23, a set screw 211 isscrewed into the tapped hole from the outer peripheral surface side, sothat the lubricant-containing polymer member 210 is fixed to the ballscrew nut 202.

Since the openings of the lubricant reserve holes 210 d are closed onthe bottom face 205 b of the recess 205, the lubricant in the lubricantreserve holes 210 d is sealed in the ball screw nut 202. The lubricantreserve holes 210 d is one example of the structures of lubricantreserve parts according to the present invention.

According to the ball screw of the structure, when the screw shaft 201makes relative rotation to the ball screw nut 202, the balls 203 in theball screw nut 202 roll on a spiral space formed by the relative threadgrooves 201 a and 202 a in the rotation direction of the screw shaft 201and circulate through a ball circulation passage (not shown). As theballs 203 roll, the ball screw nut 202 is fed in the linear directionalong the screw shaft 201. When the ball screw nut 202 and the screwshaft 201 make relative rotation, a lubricant exudes from thelubricant-containing polymer member 210 fitted into the recess 205, issupplied to the thread groove 201 b of the screw shaft 201, anduniformly covers the balls 203 rolling in the thread groove 201 b andthe thread groove 202 b of the ball screw nut for stable lubrication.Therefore, even if a lubricant is not supplied to the ball screw nut 202from the outside, the ball screw can continue good running at lowtorque.

The lubricant-containing polymer member 210 also functions as a sealmember for sealing the end of the ball screw nut 202 and shuts off theinside of the ball screw nut 202 from the external atmosphere. Thus,even if the feed screw device is used in the external atmosphere whichis of a bad environment wherein for example wood chips, etc., easilyabsorbing lubricant are existed, the inside of the ball screw nut 202 isprotected against the wood chips, etc., and the smooth lubricationeffect can be maintained over a long time.

As a lubricant exudes from the lubricant-containing polymer member 210and is consumed, the lubricant-containing polymer member 210 isreplenished with the lubricant sealed in the lubricant reserve holes 210d, so that the simple structure enables the lubricant to be sealed inthe lubricant-containing polymer member 210 and the lubricant exudesfrom the lubricant-containing polymer member 210 over a long time. Thus,the balls 203 rolling in the thread groove 201 b and the thread groove202 b of the ball screw nut can be stably lubricated for a long time.

In the lubricant-containing polymer member 210, even if foreignmaterials such as wood chips are deposited on the lubricant-containingpolymer member 210 and absorb the lubricant, the lubricant-containingpolymer member 210 is replenished with a lubricant from the lubricantreserve holes 210 d. Accordingly, it is not feared that a lubricationfailure will be invited.

FIG. 25 shows a modified example of the lubricant-containing polymermember 210 of the eighth embodiment shown in FIG. 24.

A modified example lubricant-containing polymer member 214 is also anelastic member formed like a cylindrical shape and having a cut part 214a along the substantially axial direction, and contains a lubricant suchas grease or mineral oil by a molding method similar to that of thelubricant-containing polymer member 210.

The lubricant-containing polymer member 214 is formed on an innerperipheral surface with a projection stripe 214 b to be fitted into thethread groove 201 b of the screw shaft 201, and the lubricant-containingpolymer member 214 is formed in one end face 214 c with a lubricantreserve peripheral groove 214 d continuously extending in thecircumferential direction.

The lubricant reserve peripheral groove 214 d is filled with alubricant. An outer peripheral surface 214 e of the lubricant-containingpolymer member 214 is abutted against an inner peripheral surface 205 aof the recess 205 made in an end face of the ball screw nut 202. One endface 214 c of the lubricant-containing polymer member 214 is abuttedagainst a bottom face 205 b of the recess 205. In this state, theprojection stripe 214 b is fitted into the thread groove 201 b of thescrew shaft 201, so that the lubricant-containing polymer member 214 isfitted into the recess 205. The lubricant-containing polymer member 214is fixed to the ball screw nut 202 by the set screw 211 shown in FIG.23.

Since the groove opening of the lubricant reserve peripheral groove 214d made in the one end face 214 c is closed on the bottom face 205 b ofthe recess 205, the lubricant in the lubricant reserve peripheral groove214 d is sealed in the ball screw nut 202. This lubricant reserveperipheral groove 214 d is one example of structure of the lubricantreserve part according to the present invention.

The lubricant-containing polymer member 214 also functions as a sealmember for sealing the end of the ball screw nut 202 and shuts off theinside of the ball screw nut 202 from the external atmosphere. Thus,even if the feed screw device is used in the external atmosphere whichis of a bad environment wherein wood chips, etc., easily absorbinglubricant are existed, the inside of the ball screw nut 202 is protectedagainst such bad environment, so that the smooth lubrication effect canbe maintained over a long time.

As a lubricant exudes from the lubricant-containing polymer member 214and is consumed, the lubricant-containing polymer member 214 isreplenished with the lubricant sealed in the lubricant reserveperipheral groove 214 d, so that the lubricant exudes from thelubricant-containing polymer member 214 over a long time. Thus, theballs 203 rolling in the thread groove 201 b and the thread groove 202 bof the ball screw nut can be stably lubricated for a long time.

Even if foreign materials such as wood chips are deposited on thelubricant-containing polymer member 214 and absorb the lubricant, thelubricant-containing polymer member 214 is replenished with a lubricantfrom the lubricant reserve peripheral groove 214 d, thus it is notfeared that a lubrication failure will be invited.

FIG. 26 is a sectional view to show the main part of a ball screwaccording to a ninth embodiment of the invention. FIG. 27 is aperspective view to show a lubricant-containing polymer member used inthe ninth embodiment. Components identical with those previouslydescribed with reference to FIGS. 23 to 25 in the eighth embodiment aredenoted by the same reference numerals in FIGS. 26 and 27 and will notbe discussed again.

In the ninth embodiment, a lubricant-containing polymer member 216fitted into an annular recess 205 is an elastic member formed into acylindrical shape and having a cut part 216 a along the substantiallyaxial direction, as shown in FIG. 27, and contains a lubricant such asgrease or mineral oil as in the eighth embodiment. Thelubricant-containing polymer member 216 is formed on an inner peripheralsurface with a projection stripe 216 b fitted into a thread groove 201 bof a screw shaft 201 and formed in an outer peripheral surface 216 ewith a plurality of lubricant reserve holes 216 d at positions distantfrom each other in the circumferential direction.

The lubricant reserve holes 216 d are filled with a lubricant, the outerperipheral surface 216 e of the lubricant-containing polymer member 216is abutted against an inner peripheral surface 205 a of the recess 205made in a ball screw nut 202, and one end face 216 c of thelubricant-containing polymer member 216 is abutted against a bottom face205 b of the recess 205. In this state, the projection stripe 216 b isfitted into the thread groove 201 b of the screw shaft 201, so that thelubricant-containing polymer member 216 is fitted into the recess 205,as shown in FIG. 26. Set screws 211 are screwed into tapped holes madetoward the recess 205 of the ball screw nut 202, so that the tips of theset screws 211 are engaged into the lubricant reserve holes 216 d forfixing the lubricant-containing polymer member 216 to the ball screw nut202.

Since the openings of the lubricant reserve holes 216 d are closed onthe inner peripheral surface 205 a of the recess 205, the lubricant inthe lubricant reserve holes 216 d is sealed in the ball screw nut 202.The lubricant reserve holes 216 d is one example of structure of thelubricant reserve part according to the present invention.

According to the ball screw of the structure, when the screw shaft 201makes relative rotation to the ball screw nut 202, the balls 203 in theball screw nut 202 roll on a spiral space formed by the relative threadgrooves 201 a and 202 a in the rotation direction of the screw shaft 201and circulate through a ball circulation passage (not shown). As theballs 203 roll, the ball screw nut 202 is fed in the linear directionalong the screw shaft 201. When the ball screw nut 202 rotates, alubricant exudes from the lubricant-containing polymer member 216 fittedinto the recess 205, is supplied to the thread groove 201 b of the screwshaft 201, and uniformly covers the balls 203 rolling in the threadgroove 201 b and the thread groove 202 b of the ball screw nut forstable lubrication. Therefore, even if a lubricant is not supplied tothe ball screw nut 202 from the outside, the ball screw can continuegood running at low torque.

The lubricant-containing polymer 216 also functions as a seal member forsealing the end of the ball screw nut 202 and shuts off the inside ofthe ball screw nut 202 from the external atmosphere. Thus, even if thefeed screw device is used in the external atmosphere which is of a badenvironment wherein for example wood chips, etc., easily absorbinglubricant are existed, the inside of the ball screw nut 202 is protectedagainst the wood chips, etc., and the smooth lubrication effect can bemaintained over a long time.

As a lubricant exudes from the lubricant-containing polymer member 216and is consumed, the lubricant-containing polymer member 216 isreplenished with the lubricant sealed in the lubricant reserve holes 216d, so that the lubricant exudes from the lubricant-containing polymermember 216 over a long time. Thus, the balls 203 rolling in the threadgroove 201 b and the thread groove 202 b of the ball screw nut can bestably lubricated for a long time.

Even if foreign materials such as wood chips are deposited on thelubricant-containing polymer member 216 and absorb the lubricant, thelubricant-containing polymer member 216 is replenished with a lubricantfrom the lubricant reserve holes 216 d, thus it is not feared that alubrication failure will be invited.

FIG. 28 shows a modified example of the lubricant-containing polymermember 216 of the ninth embodiment shown in FIG. 27.

A modified example lubricant-containing polymer member 218 is also anelastic member formed into a cylindrical shape and having a cut part 218a along the substantially axial direction, and contains a lubricant suchas grease or mineral oil by a molding method similar to that of thelubricant-containing polymer member 216.

The lubricant-containing polymer member 218 is formed on an innerperipheral surface with a projection stripe 218 b fitted into the threadgroove 201 b of the screw shaft 201 and formed in an outer peripheralsurface 218 e with a lubricant reserve peripheral groove 218 dcontinuous in the circumferential direction.

As similar to the lubricant reserve peripheral groove 216 d shown inFIG. 26, the lubricant reserve peripheral groove 218 d is filled with alubricant, an outer peripheral surface 218 e of the lubricant-containingpolymer member 218 is abutted against an inner peripheral surface 205 aof the recess 205 made in the ball screw nut 202, and one end face 218 cof the lubricant-containing polymer member 218 is abutted against abottom face 205 b of the recess 205. In this state, the projectionstripe 218 b is fitted into the thread groove 201 b of the screw shaft201, so that the lubricant-containing polymer member 218 is fitted intothe recess 205. A set screw 211 is screwed into the lubricant reserveperipheral groove 218 d for fixing the lubricant-containing polymermember 218 to the ball screw nut 202.

Since the groove opening of the lubricant reserve peripheral groove 218d made in the outer peripheral surface 218 e of the lubricant-containingpolymer member 218 is closed on the inner peripheral surface 205 a ofthe recess 205, the lubricant in the lubricant reserve peripheral groove218 d is sealed in the ball screw nut 202. The lubricant reserveperipheral groove 218 d is one example of the structures of lubricantreserve part according to the present invention.

The lubricant-containing polymer member of the structure can provide thefunction and effects similar to those of the above-described embodiment.

Even if foreign materials such as wood chips are deposited on thelubricant-containing polymer member 218 and absorb the lubricant, thelubricant-containing polymer member 218 is replenished with a lubricantfrom the lubricant reserve holes 218 d, thus it is not feared that alubrication failure will be invited.

FIG. 29 is a sectional view to show the main part of a ball screwaccording to a tenth embodiment of the invention. Components identicalwith those previously described with reference to FIGS. 23 to 25 in theeighth embodiment are denoted by the same reference numerals in FIG. 29and will not be discussed again.

In the tenth embodiment, a lubricant-containing polymer member 220 isfitted into an annular recess 205. The lubricant-containing polymermember 220 has the same structure as the lubricant-containing polymermember 210 shown in FIG. 24 except that it is formed with a plurality oflubricant reserve holes 220 d filled with a lubricant in thecircumferential direction of an opposed end face 220 f. The rightopening of the lubricant-containing polymer member 220 (in FIG. 29) issealed by a reinforcing plate 222.

The reinforcing plate 222 is a disk member made of a material of a steelplate, hard rubber, plastic plate, etc., and formed with an insertionhole 222 a for a screw shaft 201 at the position of the center of axle.It has an outer peripheral diameter set slightly smaller than the outerperipheral diameter of the end face of a ball screw nut 202, and theinsertion hole 222 a is set slightly larger than the outer diameter ofthe screw shaft 201. While pressing the lubricant-containing polymermember 220 against a bottom face 205 b of the recess 205, thereinforcing plate 222 is fixed to the ball screw nut 202 by set screws224 indicated by alternate long and short dash lines in FIG. 29.

Since the openings of the lubricant reserve holes 222 d are closed onthe reinforcing plate 222, the lubricant in the lubricant reserve holes222 d is sealed in the reinforcing plate 222 integral with the ballscrew nut 202. The lubricant reserve holes 222 d is one example of thestructures of lubricant reserve parts according to the presentinvention.

The lubricant-containing polymer member of the structure can provide thefunction and effects similar to those of the above-described embodiment.

As the effect proper to the embodiment, the lubricant-containing polymermember 220 is shut off from the external atmosphere by the reinforcingplate 222, so that wood chips, dust, etc., can be prevented fromentering the lubricant-containing polymer member 220; it is not fearedthat the lubricant is absorbed into wood chips, dust, etc., from theportion.

Since the lubricant-containing polymer member 220 is held down by thereinforcing plate 222 from the opening of the recess 205 (right in FIG.29), an adhesion problem need not be considered. Thelubricant-containing polymer member 220 can be adjusted in hardness andinsufficient strength by press pressure received from the reinforcingplate 222, thus breakage, cracks, etc., can be prevented from occurring.

Further, in the embodiment, if the lubricant sealed in the lubricantreserve holes 222 d becomes insufficient, the lubricant reserve holes222 d can be easily replenished with a lubricant simply by loosening theset screws 224 and removing the reinforcing plate 222 from the ballscrew nut 222.

The embodiment uses the lubricant-containing polymer member 220 formedin the opposed end face 220 f with a plurality of lubricant reserveholes 220 d. However, if a lubricant-containing polymer member 220formed in the opposed end face 220 f with a lubricant reserve peripheralgroove continuous in the circumferential direction (member similar tothe lubricant-containing polymer member 214 shown in FIG. 25) is used,the function and effects similar to those of the embodiment can beprovided.

FIG. 30 is a sectional view to show the main part of a ball screwaccording to an eleventh embodiment of the invention.

In the embodiment, the lubricant-containing polymer member 216 formed inthe outer peripheral surface 216 e with a plurality of lubricant reserveholes 216 d shown in FIG. 27 is fitted into an annular recess 205, andthe right opening of the lubricant-containing polymer member 216 (inFIG. 30) is sealed by a reinforcing plate 222.

The lubricant-containing polymer member of the structure can provide thefunction and effects similar to those of the above-described embodiment.

The embodiment uses the lubricant-containing polymer member 216 formedin the outer peripheral surface 216 e with a plurality of lubricantreserve holes 216 d. However, if the lubricant-containing polymer member218 shown in FIG. 28, namely, member formed in the outer peripheralsurface 218 e with the lubricant reserve peripheral groove 218 d isused, the function and effects similar to those of the embodiment can beprovided.

Lubricant-containing polymer members 230A, 230B, and 230C shown in FIGS.31 to 33 are modified examples of the lubricant-containing polymermembers 210, 214, and 216 respectively shown in FIGS. 24 and 25 to 27.

The lubricant-containing polymer member 230A, 230B, 230C is formed withmicroscopic communication holes 230 a, 230 b, 230 c for communicatinglubricant reserve holes 210 d and a projection stripe 210 b, a lubricantreserve peripheral groove 214 d and a projection stripe 214 b, lubricantreserve holes 216 d and a projection stripe 216 b. Slit-like orsmall-hole-like outflow openings 230 a 1, 230 b 1, 230 c 1 are made inthe projection stripe 210 b, 214 b, 216 b.

With a ball screw using the lubricant-containing polymer member 230A ofthe structure, a lubricant sealed in the lubricant reserve holes 210 dflows out directly into the outflow opening 230 a 1 through thecommunication hole 230 a. Thus, if much lubricant is required to providestable lubrication, the lubricant-containing polymer member 230A becomesan optimum member. With another lubricant-containing polymer member 230B(230C), a lubricant sealed in the lubricant reserve peripheral groove214 d (lubricant reserve holes 216 d) flows out directly into theoutflow opening 230 b 1 (230 c 1) through the communication hole 230 b(230 c). Thus, similar effects to those of the lubricant-containingpolymer member 230A can be provided.

FIG. 34 shows a single axis actuator comprising the ball screws of theembodiments. The single axis actuator comprises a ball screw nut (notshown) in a slider 34 disposed for relative rotation via balls in ascrew shaft 1 having both ends supported for rotation. Reference numeral36 is a ball circulation section for guiding a large number of ballsinto thread grooves of the screw shaft 1 and the ball screw nut andcirculating the balls. A lubricant-containing polymer member 40 to whicha reinforcing plate is attached, fixed by a set screw 38 is disposed atposition A outside the ball circulation section 36. Alubricant-containing polymer member 40 to which a reinforcing plate isattached is also disposed at position B facing position A with theslider 34.

FIGS. 35 and 36 show the lubricant-containing polymer member 40 usedwith the single axis actuator. The lubricant-containing polymer member40 is formed with a lubricant reserve peripheral groove 40 a similar tothat of the member, for example, shown in FIG. 25 and lubricant reserveholes 40 b similar to those of the member, for example, shown in FIG. 24at positions distant from the lubricant reserve peripheral groove 40 a.The lubricant reserve peripheral groove 40 a and the lubricant reserveholes 40 b are filled with a lubricant. As the lubricant exudes from thelubricant-containing polymer member 40 and is consumed, the lubricantreserve peripheral groove 40 a and the lubricant reserve holes 40 b arereplenished with a lubricant.

If the lubricant-containing polymer member 40 comprises the lubricantreserve peripheral groove 40 a and the lubricant reserve holes 40 b aslubricant reserve parts as described above, the invention can alsoproduce the function and effects similar to those of the embodiments.

In the embodiments, we have discussed the ball screws, but the inventionis not limited to them; if the invention is applied to slide screwsadopting angular screws, etc., similar function and effects can beprovided.

Next, a modified example of the lubricant-containing polymer member 230Cshown in FIG. 33 will be discussed with reference to FIG. 37.

As shown in FIG. 37, a lubricant-containing polymer member 330C has thesame structure as the lubricant-containing polymer member 230C exceptthat it is not formed with the projection stripe 216 b. An innerperipheral surface 330 a of the lubricant-containing polymer member 330Ccomes in direct contact with the outer peripheral surface 201 a of thescrew shaft 201, so that a lubricant exudes onto the outer peripheralsurface 201 a gradually with rotation of the screw shaft. Thelubricant-containing polymer member 330C is formed with a microscopiccommunication hole 330 b for communicating a lubricant reserve groove316 d and the inner peripheral surface 330 a. A lubricant is suppliedfrom the lubricant reserve groove 316 d directly to the outer peripheralsurface 201 a of the screw shaft 201 through the communication hole 330b. As the lubricant is directly supplied, more stable lubrication isprovided.

Further, a modified example of the lubricant-containing polymer member230B shown in FIG. 32 will be discussed with reference to FIG. 38.

As shown in FIG. 38, a lubricant-containing polymer member 330B has thesame structure as the lubricant-containing polymer member 230C exceptthat it is not formed with the projection stripe 214 b. An innerperipheral surface 331 a of the lubricant-containing polymer member 330Bcomes in direct contact with the outer peripheral surface 201 a of thescrew shaft 201, so that a lubricant exudes onto the outer peripheralsurface 201 a gradually with rotation of the screw shaft. Thelubricant-containing polymer member 330B is formed with a microscopiccommunication hole 331 b for communicating a lubricant reserveperipheral groove 314 d and the inner peripheral surface 330 a. Alubricant is supplied from the lubricant reserve peripheral groove 314 ddirectly to the outer peripheral surface 201 a of the screw shaft 201through the communication hole 330 b. As the lubricant is directlysupplied, more stable lubrication is provided.

Further, a modified example of the lubricant-containing polymer member230B shown in FIG. 32 will be discussed with reference to FIG. 39.

As shown in FIG. 39, a lubricant-containing polymer member 332B has thesame structure as the lubricant-containing polymer member 230C exceptthat it comprises a seal member 333 fitted into the opening of thelubricant reserve peripheral groove 214 d for sealing a lubricant. Theseal member 333 is made of the same material as the lubricant-containingpolymer member 332B. Alternatively, the seal member 333 may be made of aplastic or metal.

Next, a modified example of the lubricant-containing polymer member 230Bshown in FIG. 32 will be discussed with reference to FIG. 40.

As shown in FIG. 40, a lubricant-containing polymer member 334B has thesame structure as the lubricant-containing polymer member 230B exceptfor the placement position of the lubricant reserve peripheral groove314 d. The lubricant-containing polymer member 334B has a lubricantreserve peripheral groove 314 d pulled to the side of the outerperipheral surface 201 a of the screw shaft 201, that is, thelubricant-containing polymer member 334B has the lubricant reserveperipheral groove 314 d which is shifted to the diametric inside as muchas possible for increasing elasticity, so that a lubricant easily exudesfrom the lubricant reserve peripheral groove 314 d and is easilysupplied to the outer peripheral surface 201 a of the screw shaft 201.

Further, a modified example of the lubricant-containing polymer member330C shown in FIG. 37 will be discussed with reference to FIG. 41.

As shown in FIG. 41, a lubricant-containing polymer member 335B has thesame structure as the lubricant-containing polymer member 330C exceptthat a groove 336 extending in the circumferential direction is made inan inner peripheral surface 330 a. Since the groove 336 extending in thecircumferential direction is made in the inner peripheral surface 330 a,the lubricant-containing polymer member 335B has the inner peripheralthinner than the outer periphery and a lubricant sealed in a lubricantreserve peripheral groove 314 d exudes to the inner periphery moreeasily than to the outer periphery and thus is easily supplied to theouter peripheral surface 201 a of the screw shaft 201.

As we have discussed, when the feed screw device of the invention isdriven, a lubricant in the lubricant supply device exudes gradually withrotation of the screw shaft and is automatically supplied to the feedscrew device. Resultantly, even if a lubricant is not supplied from theoutside, the feed screw device can continue good running for a long timeat low torque.

Particularly, since a lubricant need not be supplied from the outside,the feed screw device can be used as effective lubrication means in asystem that can use only an extremely small amount of lubricant, such asa semiconductor manufacturing system.

Moreover, in the feed screw device of the invention, the innerperipheral surface of the lubricant supply device can be brought intoreliable contact with the outer peripheral surface of the screw shaft bysimple means and the outer diameter of the feed screw device is not madelarge.

Moreover, in the feed screw device of the invention, jump out of thelubricant supply device from the nut member and rotation with the screwshaft can be prevented.

In the screw transmission device of the invention, the inner diameter ofthe lubricant supply device is reduced by simple means for uniformcontact with the screw shaft; a lubricant can be supplied well and wearon one side can be prevented.

As we have discussed, according to the feed screw device of theinvention, the lubricant-containing polymer member seals both the endsof the screw nut and shuts off the inside of the screw nut from theexternal atmosphere, so that even if the feed screw device is used inthe external atmosphere which is of a bad environment wherein forexample, wood chips, etc., easily absorbing lubricant are existed, theinside of the screw nut is protected against the wood chips, etc., andthe smooth lubrication effect can be maintained over a long time.

As a lubricant exudes from the lubricant-containing polymer member andis consumed, the lubricant-containing polymer member is replenished witha new lubricant sealed in the lubricant reserve parts, thus thelubricant exudes from the lubricant-containing polymer member over along time and stable lubrication can be carried out for a long time.

Further, even if foreign materials such as wood chips are deposited onthe lubricant-containing polymer member and absorb the lubricant, thelubricant-containing polymer member is replenished with a lubricant fromthe lubricant reserve parts, thus it is not feared that a lubricationfailure will be invited.

What is claimed is:
 1. A feed screw device comprising: a screw shaft; anut member threadably engaging an outer periphery surface of said screwshaft; a lubricant supply device contacting the outer peripheral surfaceof said screw shaft; and a cap-shaped member which is secured to saidnut member and houses said lubricant supply device, said nut memberbeing positioned outside of said cap-shaped member, wherein saidcap-shaped member is disposed to project from an axial end surface ofthe nut member and along an outer circumferential surface of thelubricant supply device, said outer circumferential surface extends in alongitudinal direction of said screw shaft, and wherein said lubricantsupply device contains lubricant and is disposed between an end face ofsaid cap-shaped member and said axial end surface of said nut member,said end face of said cap-shaped member extends toward said screw shaftand covers at least a portion of said lubricant supply device.
 2. Thefeed screw device according to claim 1, wherein said lubricant supplydevice has an insertion hole formed in a side thereof.
 3. The feed screwdevice according to claim 2, further including a projection formed onsaid cap-shaped member, said projection being received in said insertionhole.
 4. The feed screw device according to claim 3, wherein saidprojection is formed on a bottom wall portion of said cap-shaped member.5. The feed screw device according to claim 3, wherein said projectionis formed on a cirumferential wall portion of said cap-shaped member. 6.The feed screw device according to claim 3, wherein said projectionformed on said cap-shaped member prevents said lubricant supply devicefrom rotating with said screw shaft.
 7. The feed screw device accordingto claim 6, wherein said cap-shaped member is fixedly secured to saidnut member by a screw.
 8. The feed screw device according to claim 1,further including a projection formed on an inner peripheral surface ofsaid lubricant supply device which engages with said screw shaft.
 9. Thefeed screw device according to claim 8, wherein said projection forms aspiral configuration, said spiral configuration fits into a threadgroove of said screw shaft.
 10. The feed screw device according to claim1, wherein at least a portion of said lubricant supply device facingsaid screw shaft is made of one of rubber and synthetic resin.
 11. Afeed screw device comprising: a screw shaft; a nut member threadablyengaging an outer periphery surface of said screw shaft; a lubricantsupply device contacting the outer peripheral surface of said screwshaft; and a cap-shaped member which is secured to said nut member andhouses said lubricant supply device, said nut member being positionedoutside of said cap-shaped member, wherein said cap-shaped membercomprises a cylindrical portion covering an outer circumferentialsurface of the lubricant supply device, said outer circumferentialsurface extends beyond an end face of said nut member, and wherein saidlubricant supply device contains lubricant and is disposed between anend face of said cap-shaped member and an axial end surface of said nutmember, said end face of said cap-shaped member extends toward saidscrew shaft and covers at least a portion of said lubricant supplydevice.
 12. A feed screw device comprising: a screw shaft; a nut memberthreadably engaging an outer periphery surface of said screw shaft; alubricant supply device contacting the outer peripheral surface of saidscrew shaft; and a cap-shaped member which is secured to said nut memberand houses said lubricant supply device, said cap-shaped memberincludes, an outwardly extending flange which is fastened to an axialend surface of the nut member; a cylindrical portion which extends awayfrom said nut member; an end face which covers an axial end of saidlubricant supply device; and a projection which is inserted into thelubricant supply device so as to hold the lubricant supply device,wherein said lubricant supply device contains lubricant and is disposedbetween said end face of said cap-shaped member and said axial endsurface of said nut member, said end face of said cap-shaped memberextends toward said screw shaft and covers at least a portion of saidlubricant supply device.
 13. A feed screw device comprising: a screwshaft; a nut member threadably engaging an outer periphery surface ofsaid screw shaft; a lubricant supply device contacting the outerperipheral surface of said screw shaft; and a cap-shaped member which issecured to said nut member and houses said lubricant supply device,wherein said cap-shaped member has an outwardly extending flange whichis fastened to an axial end of said nut member, and a cylindricalportion which extends away from said nut member so as to surround saidlubricant supply device, said cap-shaped member also having a projectionwhich extends into and holds said lubricant supply device, and whereinsaid lubricant supply device contains lubricant and is disposed betweenan end face of said cap-shaped member and an axial end surface of saidnut member, said end face of said cap-shaped member extends toward saidscrew shaft and covers at least a portion of said lubricant supplydevice.
 14. The feed screw device according to claim 1, wherein saidcap-shaped member includes, an outwardly extending flange which isfastened to an axial end surface of the nut member; a cylindricalportion which extends away from said nut member; an end face whichcovers an axial end of said lubricant supply device; and a projectionwhich is inserted into the lubricant supply device so as to hold thelubricant supply device.
 15. The feed screw device according to claim11, wherein said cap-shaped member has an outwardly extending flangewhich is fastened to an axial end of said nut member, and a cylindricalportion which extends away from said nut member so as to surround saidlubricant supply device, said cap-shaped member also having a projectionwhich extends into and holds said lubricant supply device.
 16. The feedscrew device according to claim 3, wherein said projection is formedfrom a cut out portion of said cap-shaped member which is bent towardsaid lubricant supply device, and is integrally formed on saidcap-shaped member.
 17. The feed screw device according to claim 12,wherein said projection is formed from a cut out portion of saidcap-shaped member which is bent toward said lubricant supply device, andis integrally formed on said cap-shaped member.
 18. The feed screwdevice according to claim 13, wherein said projection is formed from acut out portion of said cap-shaped member which is bent toward saidlubricant supply device, and is integrally formed on said cap-shapedmember.
 19. The feed screw device according to claim 14, wherein saidprojection is formed from a cut out portion of said cap-shaped memberwhich is bent toward said lubricant supply device, and is integrallyformed on said cap-shaped member.
 20. The feed screw device according toclaim 1, wherein said lubricant supply device comprises a plurality oflip parts projecting toward said screw shaft and which come in slidingcontact with the outer peripheral surface of said screw shaft.